The two badges that got removed are as follows.
Impossible badge - get 700 headshots in one game in last stand.
This got editted to hard badge so that people could still get it but would get less points, those lucky enough to get it before it changed kept their points. I personally was crap at last stand and didn't manage to get it before they changed it.
This impossible (700 headshoots, which I got) was changed to one medium (complete the game) and one hard (500 headshoots)
It got changed because you could get 99 shoots with the rifle (glitch which still works, I think) and because you could replay the last day to get enough headshoots (just die with 1 zombie remaining and replay), which made it an easy impossible badge.